Inter-RAT Hand-off Trigger Using Distance Thresholds
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Solution Overview
Problem
Conventional methods for inter-RAT idle hand-off in mobile stations are prone to 'ping-pong' issues due to unreliable power measurements caused by shadowing and fading, and fail to trigger hand-offs at the right time or place, especially when moving off the edge of a border sector, leading to inefficient and frequent registrations.
Innovation Solution
A method that triggers a mobile station to acquire synchronization with a second carrier if it enters a border area and measures channel conditions, including reverse link power and distance from the serving base station, to determine when to initiate an inter-RAT hand-off, ensuring efficient hand-off by setting threshold values for channel and distance criteria.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If power measurement with hysteresis is used to trigger idle hand-off, then ping-pong issue is reduced, but reliability is worsened due to shadowing and fading in mobile environment
Solution Approach 1:
The patent changes the triggering parameter from power measurement to distance measurement. By using distance thresholds instead of power thresholds, the system avoids the reliability issues of power measurements caused by shadowing and fading, while maintaining hand-off stability through consistent distance-based criteria.
Solution Approach 2:
The patent substitutes the mechanical/power-based measurement system with a geometric/distance-based system. Instead of measuring signal power which is affected by environmental factors, the system measures distance to the base station using timing advance or other distance estimation methods, which are more reliable and consistent.
2Productivity
If forward link signal-to-noise ratio measurement is used for hand-off trigger, then hand-off decision is made, but hand-off timing is inaccurate when mobile station is at coverage edge
Solution Approach 1:
The patent changes the measurement parameter from forward link signal-to-noise ratio to reverse link power or distance. This parameter change allows accurate hand-off triggering at coverage edges because reverse link measurements reflect the actual uplink quality and distance, which are critical for determining whether the mobile station is truly at the edge of coverage.
Solution Approach 2:
The patent inverts the measurement direction by using reverse link measurements instead of forward link measurements. By measuring the reverse link quality and distance from the mobile station to the base station, the system gains accurate information about the mobile's actual position and link quality, enabling correct hand-off decisions at coverage boundaries.
3Stability of the object's composition
If secondary color code method with spatial hysteresis is used, then ping-pong issue at sub-net boundary is resolved, but device complexity increases due to cross sub-net paging requests
Solution Approach 1:
The patent extracts the hand-off trigger mechanism from the complex secondary color code system and implements a simpler distance-based trigger. By using straightforward distance thresholds to determine when to initiate hand-off preparation, the system achieves boundary stability without requiring complex cross sub-net paging procedures.
Solution Approach 2:
The patent applies preliminary action by triggering hand-off preparation when the mobile station enters a border area or exceeds a distance threshold, rather than waiting for the complex secondary color code conditions to be met. This early triggering simplifies the overall process by initiating synchronization and measurement procedures before the actual hand-off is needed.
Data Source
AI summary
A method for hand-off trigger at access technology borders may include triggering a mobile station in communication with a first carrier having a first technology type to acquire synchronization with a second carrier having a second technology type if the mobile station enters a border area, the border area including at least one sector covered by at least two carriers having different Radio Access Technologies (RATs) including the first technology type and the second technology type.